Highly efficient power amplifiers operating at low voltages are required for many portable applications. At RF and microwave frequencies, power added efficiency can be improved, for example, by designing Class B, Class C, or Class E type power amplifiers. However, digital modulation schemes used in modern communication circuits require high efficiency amplifiers with high linearity. It has been shown that Class E amplifiers provide a higher efficiency and a better overall linearity than Class B or Class C amplifiers. Moreover, Class E power amplifiers, maintain the higher efficiency for larger range of output power.
However, as will be explained in more detail below, Class E amplifiers still have room for improvement. Specifically, the major power loss in an amplifier is the power dissipated by the output device.
Accordingly, it is highly desirable to provide power amplifiers with improved efficiency while retaining at least the present linearity.
It is a purpose of the present invention to provide a new and improved high efficiency power amplifier.
It is another purpose of the present invention to provide a new and improved high efficiency power amplifier which operates more efficiently than prior devices at higher frequencies.
It is still another purpose of the present invention to provide a new and improved high efficiency power amplifier with fewer tuning elements and smaller size.